The present invention relates to a plastic lens material, a production process of the material, a plastic lens composition containing the material, a plastic lens obtained by curing the composition, and a production process of the plastic lens.
More specifically, the present invention relates to a plastic lens material which can produce a plastic lens while preventing the generation of uneven dyeing and which can be used for a plastic lens composition capable of preventing damaging of a mold used for the cast polymerization; a production process of the material; a plastic lens composition containing the material; a plastic lens obtained by curing the composition; and a production process of the plastic lens.
Recently, organic glass has been widely used for optical materials for cameras, televisions, prisms, telescopes and ophthalmic lenses. In particular, inorganic glass for ophthalmic lenses is being replaced by organic glass and, particularly, by plastic lenses. Under these circumstances, the plastic lens is required to be low in the weight, facilitated in the molding, and favored with good dyeability, evenly dyeable.
Representative examples of the resin conventionally used as a raw material for plastic lenses include polystyrene resin, polycarbonate resin, polymethyl methacrylate resin and polydiethylene glycol bis(allyl carbonate) resin. The physical properties and production methods of these resins have hitherto been known and are described in detail in, for example, Plastic Age, Vol. 35, pp. 198-202 (1989).
In this publication, the properties of the plastic lens derived from each resin are described as follows. The plastic lens derived from polystyrene resin has a problem in that a sufficiently high value cannot be obtained with respect to the birefringence and light scattering, though the refractive index is high. The plastic lens derived from polycarbonate resin is disadvantageously inferior in solvent resistance and scratch resistance, though the impact resistance are high. In the plastic lens derived from polymethyl methacrylate resin, the refractive index is low and the impact resistance are not at a satisfactory level.
Other than these, a plastic lens derived from polydiethylene glycol bis(allyl carbonate) resin is known (see, for example, EP 0473163A). This plastic lens is favored with superior properties particularly as a plastic lens for eyeglasses, such as excellent impact resistance and high Abbe number, despite the low refractive index of 1.498, therefore, this is most frequently used.
The polydiethylene glycol bis(allyl carbonate) resin is advantageous in that the polymerization reaction is easy to control because the polymerization reaction proceeds at a low speed as compared with acrylic resin.
Therefore, a uniform polymerization reaction can be attained and, by virtue of this, the plastic lens derived from the polydiethylene glycol bis(allyl carbonate) resin is reduced in optical strain.
The plastic lens derived from polydiethylene glycol bis(allyl carbonate) resin is also known to have excellent dyeing properties such that when the lens is dyed according to a general technique of dipping a plastic lens obtained by casting in a dyeing solution at a high temperature, the dyeing density is higher than those of plastic lenses derived from other resins.
However, the plastic lens derived from polydiethylene glycol bis(allyl carbonate) resin has a problem in that when the lens is polymerized in a mold for lenses and then the cured product is separated from the mold, the mold is damaged.
In general, a plastic lens is manufactured by so-called cast polymerization where a monomer is polymerized using two glass molds. The molds must be cleaned after casting and cleaning is usually performed using a strong alkaline solution or a strong acid. Unlike metal, glass is scarcely changed in quality by cleaning, therefore, glass is preferably used. Furthermore, glass can be easily polished and thereby extremely reduced in the surface roughness.
In the polymerization process, curing shrinkage generally occurs. On the other hand, the lens is required to perfectly imitate the curve of the glass surface and to this purpose, the monomer must exhibit good adhesion to the glass during the polymerization.
After the polymerization of monomer, the lens is disengaged from the glass mold. This process actually proceeds as follows. The mold is pried open by a wedge.
At this time, a very great energy is released and occasionally even a shock may be caused.
This releasing with such a force sometimes damages the glass mold. More specifically, the glass mold is partly drawn out and cannot be used as a glass mold any more. This phenomenon randomly occurs in the production of lenses. The loss caused by this usually reaches several % of the production yield of plastic lenses.
In order to decrease such damage to the mold, a slight amount of a mold-releasing agent is added in some cases, however, this adversely affects other properties of the lens, for example, adhesion of a scratch-resistant coating which is applied in the next step. Accordingly, the use of a mold-releasing agent is not proper for solving this problem.
Techniques for overcoming this problem are disclosed in JP-W-10-513574 (the term xe2x80x9cJP-Wxe2x80x9d as used herein refers to a xe2x80x9cJapanese Unexamined Patent Publication of International Patent Applicationxe2x80x9d) and International Patent Publications WO99/17137 and WO99/38899.
JP-W-10-513574 discloses use of a diallyl phthalate oligomer, whereby the problem of damaging the mold at the releasing can be somewhat overcome. However, this technique is still not at a satisfactory level.
Furthermore, by the addition of a diallyl phthalate oligomer, the cured lens is readily increased in the refractive index and this is not preferred from the standpoint of using a mold for use in the production of a plastic lens from poly[diethylene glycol bis(allyl carbonate)] resin. In addition, there is a problem in the weather resistance.
International Patent Publications WO99/17137 and WO99/38899 disclose use of a diallyl ester oligomer containing a cyclohexane dicarboxylate structure, whereby the problem of causing damaging of the mold at the releasing can be overcome. Also, even dyeing which is another property of dyeability required for a plastic lens can be attained, that is, the technique has an improvement effect also with respect to the inhibition of uneven dyeing.
However, the diallyl ester oligomer compounds containing a cyclohexane dicarboxylate structure disclosed in these publications have a relatively high crystallinity and suffer from a problem that when stored at a normal temperature or less for a long period of time, the compound becomes white and turbid.
In such a case, if the compound is redissolved by raising the temperature using some means, the compound may be used as a raw material of a plastic lens without any problem, however, a fear still remains for possibilities that the compound structure changes due to excess heating or in turn the improvement effect intended by the addition of the compound decreases. Furthermore, an extra process of heating the compound on use is necessary and the profitability is disadvantageously low in view of the energy required.
The present invention has been made as an attempt to improve the crystallinity of the diallyl ester oligomer compounds containing a cyclohexane dicarboxylate structure by taking notice of the problem that the compound becomes white and turbid when stored at normal temperature. Accordingly, the object of the present invention is to provide a plastic lens material, a production process of the material, a plastic lens composition containing the material, a plastic lens obtained by curing the composition, and a production process of the plastic lens, in which the effect of improving the releasability of a plastic lens from a mold and also the dyeability of the plastic lens as described in WO 99/17137 and WO99/38899 can be more simply implemented.
In order to solve the above-described problems, the present inventors have made extensive investigations on various physical properties of a diallyl ester oligomer containing a cyclohexane dicarboxylate structure, on resin compositions over a wide range including additives considered to be effective in preventing the compound from becoming white and turbid, and on the compositions thereof.
As a result, it has been found that a plastic lens material free of occurrence of changing into a white and turbid material due to crystallization at room temperature can be produced by controlling the ratio of a cis structure to a trans structure in the cyclohexane dicarboxylate structural units contained in a diallyl ester oligomer compound containing cyclohexane dicarboxylate structural units.
Furthermore, it has been found that a plastic lens composition comprising the above-described material and a poly(allyl carbonate) having a specific structure, and a plastic lens obtained by curing the composition can solve at the same time the problem of uneven dyeing in a cured product. The present invention has been accomplished based on these findings.
More specifically, the present invention (I) is a plastic lens material comprising a compound containing a group represented by the following general formula (1) as a terminal group and a group represented by the following general formula (2) as a repeating unit, wherein a part or all of 1,4-cyclohexane dicarboxylate structural units are a cis structure: 
wherein each R1 independently represents an allyl group or a methallyl group and each X independently represents an organic residue derived from a polyhydric alcohol having 2 to 20 carbon atoms and containing 2 to 6 hydroxy groups, provided that X may further contain a branched structure containing a terminal group of the general formula (1) and a repeating unit of the general formula (2), through an ester bond.
Incidentally, the terms xe2x80x9ccisxe2x80x9d and xe2x80x9ctransxe2x80x9d as used herein refer to the geometrical isomerism of a compound and this is described in detail in Iwanami Rikagaku Jiten, xe2x80x9cKika Iseixe2x80x9d (Iwanami Physics and Chemistry Encyclopedia. xe2x80x9cGeometrical Isomerismxe2x80x9d), 3rd and enlarged edition (Feb. 5, 1987).
The present invention (II) is a process for producing the plastic lens material of the present invention (I), comprising the following first and second steps:
first step:
a step of reacting 1,4-cyclohexane dicarboxylic acid containing a cis structure with allyl alcohol and/or methallyl alcohol in the presence of a catalyst to obtain a 1,4-cyclohexane dicarboxylic acid ester; and
second step:
a step of performing a transesterification reaction between the 1,4-cyclohexane dicarboxylic acid ester obtained in the first step and a polyhydric alcohol in the presence of a catalyst to obtain a compound for a plastic lens material.
The present invention (III) is a composition for a plastic lens, comprising as essential components at least one plastic lens material of the present invention (I) and at least one compound represented by the following general formula (3): 
wherein Y represents one or more organic residue derived from a polyhydric saturated alcohol having 2 to 20 carbon atoms and containing 2 to 6 hydroxy groups, each R2 independently represents an allyl group or a methallyl group, provided that where the number of hydroxy groups in Y is n, s is 0 or an integer of n-1, t is an integer of 1 to n, and s+t=n.
Incidentally, the term xe2x80x9centire curable componentxe2x80x9d as used herein refers to a total amount of the plastic lens material of the present invention (I), the compound represented by the above formula (3) and a monomer copolymerizable with the plastic lens material of the present invention (I) or the compound represented by the above formula (3).
The present invention (IV) is a composition for a plastic lens according to the present invention (III), further comprising from 0.1 to 10 parts by mass of at least one radical polymerization initiator per 100 parts by mass of the composition for a plastic lens of the present invention (III).
The present invention (V) is a plastic lens obtained by curing the composition for a plastic lens of the present invention (III) or the present invention (IV).
The present invention (VI) is a production process of the plastic lens of the present invention (V).